1. Field of the Invention
The present invention relates to an image-forming process and an image-recording material. More particularly, it relates to a process for the intensification of images by an oxidationreduction reaction using at least one of chlorous acid, chlorite, chlorine dioxide water, bromite and bromous acid. Still more particularly, in an especially preferred embodiment it is concerned with a photographic image-recording material containing a photographic color former in a greater amount than the stoichiometric amount based on silver, and to a process for intensifying the images thereof.
2. Description of the Prior Art
In the field of color photography to which the present invention is applicable, cyan, yellow, magenta and like color formers are incorporated into a silver halide emulsion by various processes, and color photographic materials prepared by coating the resulting emulsion on a support are subjected, after imagewise exposure, to a series of processings to reproduce images on the photographic materials.
Fundamental steps in the processings are a color-developing step and a silver-removing step. That is, silver halide contained in an exposed silver halide color photographic material is reduced with a color developing agent in the colordeveloping step to produce silver, whereas oxidized color developing agent reacts with a coupler to provide dye images. Then, the color photographic material is subjected to silver-removing. After oxidizing silver, produced in the preceding step by the action of an oxidizing agent (usually called a bleaching agent), oxidized silver is dissolved away with a silver ion-complexing agent (usually called a fixing agent), and is thus removed from the photographic material. Accordingly, only a dye image is formed in the photographic material.
In actual development processing, auxiliary steps to maintain the photographic and physical properties of images or to improving the preservability of images are generally used in addition to the above-described two fundamental steps (color-developing and silver-removing). For example, there can be illustrated a hardening to prevent the light-sensitive film from being softened too much during processings, a stopping to effectively stop the development reaction, an image-stabilizing to stabilize images, delaminating a backing layer on a support, and the like.
This type of processing for color photographic materials has been commonly conducted in this field since the 1940's on a world-wide scale.
Color light-sensitive materials used for such a color processing generally contain about 1 g to 15 g of silver per m.sup.2 of support as silver halide. For example, most reflection image materials (color papers) contain 1 to 2.5 g of silver per m.sup.2, and most photographic materials such as color negative films and color reversal films contain 3 - 9 g silver per m.sup.2. This amount of silver is necessary to obtain the required color image density. However, from the viewpoint of saving silver and lowering production cost, a reduction in the amount of silver would be of great merit.
Various attemps have been made to reduce the amount of silver in light-sensitive materials while obtaining sufficient color density. For example, there are known processes of using a 2-equivalent coupler whose oxidation equivalent in the dyeproducing reaction is 2 (described in, for example, U.S. Pat. Nos. 3,253,924, 3,591,383, 3,311,476, 3,458,315, 3,476,563, 3,419,391, Japanese Patent Application 56,050/73, U.S. Pat. Nos. 3,369,895, 3,408,194, 3,415,562, British Pat. Nos. 1,040,710, 1,302,398, West German Pat. No. OLS 2,213,461, Japanese Patent Application No. 3,039/72, etc., using an auxiliary agent so as to raise the extinction coefficient of the color images (West German Patent OLS No. 2,238,051), and increasing the amount of dye produced by a halogenation-bleaching silver deposit (produced by color development) and again conducting color development (e.g., U.S. Pat. Nos. 2,439,901, 2,623,822, 2,814,565 and 3,372,028). The present invention relates to an improvement in processes belonging to the last-mentioned class, i.e., involving repeated color redeveloping.
In generally conducted color image-producing processings, reduction of silver salt and oxidation of a color developing agent take place and the oxidized developing agent in turn reacts with a coupler to form dye images. Therefore, the silver salt is used only once. On the other hand, in repeated color redeveloping, silver deposits are converted to silver halide through halogenation-bleaching, and color development is again conducted to thereby increase the amount of dye produced.
This process should be very advantageous since the silver halide in a light-sensitive material is theoretically used repeatedly. Actually, however, it has not yet been put into practice due to various restrictions. The restrictions include, firstly, the fact that an oxidizing agent used in re-halogenation bleaching remains in the emulsion film and causes bleach fog, i.e., oxidation coloration at silver salt-free areas, in the step of color re-development, thus seriously spoiling image quality.
Secondly, there is the disadvantage of an increased number of processing steps and disadvantages resulting therefrom. One color re-development requires a fixing step, a re-halogenation bleaching step, a color re-developing step, 2 to 3 washing steps and, desirably, a clearing bath, i.e., 5 to 7 steps in all in addition to ordinary processing steps. Therefore, the processing requires much time, which leads to disadvantages such as a reduction of the physical strength of an emulsion film, troublesome administration of processing solutions and increased chemicals costs.
Thirdly, there is the defect that, since re-halogenation bleaching is conducted prior to color re-development, the color developer is liable to be deteriorated.
Fourthly, since a strong ferricyanide bleach is used for re-halogenation bleaching, an environmental pollutant is present in the waste water, and therefore measures to remove the same become necessary.
Fifthly, the color images produced are likely to be destroyed through oxidation.
On the other hand, U.S. Pat. No. 3,674,490 describes a novel process for reducing the amount of silver halide in a light-sensitive material through a novel color intensifying process. According to this specification, image-wise distributed nuclei function as a catalyst for a peroxide compound, such as hydrogen peroxide, to initiate an oxidation reaction, and dyes are produced as a result of the oxidation reaction, thus forming color images. Since nuclei are required only as a catalyst, only a small amount of nuclei are necessary. Therefore, when silver is used as the nuclei, the intended color density can be attained by using silver salt in a much lower amount than that of the silver salt used in a conventional silver salt gelatin emulsion. In this process, a peroxide is used in the intensifying step provided after the developing step (color development). However, this process involves many defects. Firstly, peroxides, e.g., hydrogen peroxide, are extremely unstable in aqueous solution. Secondly, an increase of the intensifying time leads to a destruction of dye images. Thirdly, the intensifying causes fog.
On the other hand, U.S. Pat. No. 3,765,891 describes, as a novel intensifying process, a process of forming dyes by oxidation-reduction reaction with a cobalt (III) complex salt, e.g., by hexamminecobalt (III) chloride, using image-wise distributed nuclei as a catalyst. This process is superior in that cobalt (III) complex salts are more stable than peroxides. However, this process has the defect that, as compared with conventional intensification using peroxides, the degree of intensification is low.